SIR measure method and apparatus for the same

ABSTRACT

The invention discloses a signal-to-interference ratio (SIR) measurement method. The method measures interference power (I) of a single-path signal after the received signal is demodulated by the single-path demodulators of multipath receiving device at the receiving end. The total interference power is obtained by equipartition combining with the measured interference power of each single-path signal. The signal power (S) is obtained by measuring after maximum ratio combination of each single-path signal. The SIR of the received signal is the division of the signal power and the total interference power. An apparatus, implementing mentioned method, sets the interference power measurement-device in the RAKE combiner and the signal power measurement-device after the RAKE combiner. In this way, the interference measurement can effectively provide more information and can more really response to the channel variation.

This application is a continuation of international ApplicationPCT/CN01/00807, filed May 18, 2001, of which the entire disclosure ofthe pending, prior application is hereby incorporated by reference.

FIELD OF THE TECHNOLOGY

The present invention relates generally to CDMA mobile communicationtechnology, and more particularly to a method and apparatus of measuringsignal-to-interference ratio (SIR) at receiving end.

BACKGROUND OF THE INVENTION

SIR measurement is an important technology in a CDMA mobilecommunication system, and is mainly used in power control, softhand-over and cells search etc. The SIR measurement provides real timeand effective signal-to-interference ratio information for normaloperation of a system. Performance of a mobile communication system isdirectly affected by measurement accuracy of the SIR. Conventional SIRmeasurement can refer to article “SIR-Based Transmit Power Control ofReverse Link for Coherent DS-CDMA Mobile Radio” (IEICE TRANS. COMMUN.VOL. E81-B, NO. 7 JULY 1998). With reference to FIG. 1, the SIRmeasurement procedure can be summarized as following:

1) After passing through RAKE combiner 1 of the RAKE receiver, atransmitted multipath signal is formed a single-path signal.

2) The combined RAKE signal is sent, on the one hand, to the signalpower measurement-device 2 for signal power estimate, and on the otherhand, to the interference power measurement-device 3 for interferencepower estimate. The formulas for estimate can refer to the abovedocument.

3) The output of the signal power measurement-device 2 and interferencepower measurement-device 3 is divided by the divider 4 to obtain the SIRmeasurement value.

The conventional SIR measurement method measures SIR with thesingle-path signal after RAKE combining at receiving end. Nevertheless,the signal is transmitted with multipath and is received by multipathreceiving technology at receiving end. Therefore, the interferencemeasurement is unrealistic and part of the interference result is lost.Moreover, since a channel of the mobile communication system is aRayleigh-fading channel; when the channel is at heavy fading depth, theconventional SIR measurement method cannot really reflect channelvariation and cannot provide to the system accuracy and effectiveinformation.

SUMMARY OF THE INVENTION

The invention proposes a SIR measurement method and apparatus for thesame. The method and the apparatus can more effectively provideinformation of an interference measurement, and can make a SIRmeasurement more accurate.

The invention is a measurement method of signal-to-interference ratiofor CDMA mobile communication system. A signal is demodulated by thesingle-path demodulators in the RAKE combiner of the receiving end.After that, an interference power (I) of a single-path signal ismeasured. The measured interference power of every single-path signal issent to an equipartition combiner to form a total interference power.Diversity combination of every single-path signal is measured to obtainthe signal power (S). By dividing the measured signal power with thetotal interference power, the signal-to-interference ratio is obtained.

In the technical scheme, mentioned above, said total interference powerobtained by equipartition combination can be further processed withsmoothing filter to make the interference power and thesignal-to-interference ratio more accurate.

Said interference power measurement of a single-path signal, afterhaving been demodulated by a single-path demodulator at the receivingend, is made in every path, respectively. Said diversity combination canbe maximum ratio combination or equivalence gain combination.

The invention provides a signal-to-interference ratio measurementapparatus implementing the method, mentioned above. The apparatus atleast includes a RAKE combiner, a signal power measurement-device,interference power measurement-devices and a divider.

The RAKE combiner includes multiple single-path demodulators and adiversity combiner. All single-path signals outputted from thesingle-path demodulators are made diversity combination of multipathsignal in the diversity combiner to form a single signal, which is usedfor signal power measurement in the signal power measurement-device.

The interference power measurement-devices are multiple devices set inthe RAKE combiner. An input of every interference powermeasurement-device is connected to the output of the single-pathdemodulator, respectively. All interference power outputs measured byevery interference power measurement-device are sent to an equipartitioncombiner for equipartition combination. The output of the equipartitioncombiner and the output of the signal power measurement-device are sentto the divider for division operation to obtain a signal-to-interferenceratio.

The technical scheme mentioned above can further include a smoothingfilter. The smoothing filter input is connected to the equipartitioncombiner output. The output of the equipartition combiner is furthermade smooth processing. The output of the smoothing filter and theoutput of the signal power measurement-device are sent to the divider tomake a division operation to obtain the signal-to-interference ratio.

Said multiple interference power measurement-devices and multiplesingle-path demodulators are correspondingly connected one by one, i.e.,the output of each single-path demodulator is connected to aninterference power measurement-device. Said diversity combiner can be amaximum ratio combiner or an equivalent gain combiner.

The invention separates the measurement of a signal power (S) and theinterference power (I). This means that S is measured after combining inthe RAKE combiner and I of every path is measured before combining and atotal I is formed by equipartition combination. In this way, a SIR ismeasured.

Since the invention measures interference power I at every path in theRAKE combiner, so the interference measurement can effectively obtainmore information. Therefore, SIR value measured by the invention methodis more accurate than by the conventional method.

In addition, when the invention is used in a power control system, allthe original power control module will not be updated, so all theadvantages of the conventional power control are remained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram of the conventional SIR measurement.

FIG. 2 shows an embodiment block diagram of the invention.

FIG. 3 is a probability density diagram of transmitting power of a basestation.

FIG. 4 is a probability distribution diagram of transmitting power of abase station.

EMBODIMENTS OF THE INVENTION

The invention will be described in more detail, hereinafter, withreference to drawings.

FIG. 2 is an embodiment block diagram of the invention. The specificworking procedure of the embodiment is described in the following:

1. A transmitted signal, received by the multipath-receiving device atthe receiving end, is demodulated by the single-path demodulators 11 inRAKE combiner 1, and then an individual-path-demodulated single-pathsignal is formed.

2. The individual-path-demodulated single-path signal, on the one hand,passes through the maximum ratio combiner 13 and is combined to a finalsignal, on the other hand, passes through interference powermeasurement-device 12 to make interference power estimate. Theinterference power measurement formula is:

$\begin{matrix}{{I_{i}(K)} = {{\frac{1}{N_{pilot}}{\sum\limits_{m = 0}^{N_{pilot} - 1}{{r_{i}\left( {m,k} \right)}}^{2}}} - \left\lbrack {\frac{1}{N_{pilot}}{\sum\limits_{m = 0}^{N_{pilot} - 1}{{r_{i}\left( {m,k} \right)}}}} \right\rbrack^{2}}} & (1)\end{matrix}$

Wherein I_(i)(k) is i^(th) path noise interference power, i=1, 2 . . .n, n is the multipath number; N_(pilot) is the pilot symbol number inone frame data; r_(i)(m,k) is the amplitude of m^(th) symbol of k^(th)time slot of i^(th) path.

3. Taking average of measured interference power of every path throughthe equipartition combiner 5, the total inference power Ī is:

$\begin{matrix}{{\overset{\Cap}{I}(k)} = {\frac{1}{n}{\sum\limits_{i = 1}^{n}{I_{i}(k)}}}} & (2)\end{matrix}$

4. The output of equipartition combiner 5 is passed through thesmoothing filter 6 to smooth the interference power, functional functionof the smoothing filter is:I (k)=α I (k−1)+(1−α){circumflex over (I)}(k)  (3)

Wherein, Ī(k) is the k^(th) time slot interference power processed bythe α filter, Î(k) is the measured interference power of k^(th) timeslot, α is the regressive coefficient of the α filter. In a Rayleighchannel environment, since influence of multipath inference andmultiuser interference, the regressive coefficient should not take a toolarge value.

5. The signal power measurement uses the conventional method, i.e.,measuring after RAKE combining, the measurement formula is:

$\begin{matrix}{{S(k)} = \left\lbrack {\frac{1}{N_{pilot}}{\sum\limits_{m = 0}^{N_{pilot} - 1}{{r\left( {m,k} \right)}}}} \right\rbrack^{2}} & (4)\end{matrix}$

6. By passing the outputs of the signal power measuring device 2 andsmoothing filter 6 through divider 4, the SIR value of k^(th) time slotcan be obtained:

$\begin{matrix}{{{SIR}(k)} = \frac{S(k)}{\overset{\_}{I}(k)}} & (5)\end{matrix}$

The output of divider 4 is taken as the real SIR measuring value. Inaddition, if decreasing accurate requirement of the measuring result,then the smooth processing of the inference power measurement can beneglected.

The technical scheme, mentioned above, of the invention has been used ina WCDMA (wideband CDMA) for SIR measurement of inner-loop power control.In the down link, the pilot symbol number N_(pilot) is set to 4, themultipath number n is set to 2, and the Block Error Ratio (BLER) ofreceived signal is kept at 0.01. In the RAKE combiner module, each pathof the two paths is measured with formula (1). Then, the totalinterference power I is obtained by taking average of the measuredresults with formula (2). The signal power S is obtained by measuringthe data signal after RAKE combining. The ratio of the signal power andinterference power is the SIR measured value for inner-loop power.Con-paring the SIR measured value and the SIR threshold-value obtainedby outer-loop power control, a power control command is obtained. Inthis way, the power control of down link is performed.

Under the same condition, by using the SIR measurement method of theinvention and the conventional SIR measurement method, respectively, apower control simulation of down link is made, and the power controlperformance is shown in Table 1 below.

TABLE 1 SIR measurement Consistency power method Unit Average power 50%90% 95% Method of the dB −20.55 −22.2 −19.1 −18.1 invention ConventionalSIR dB −20.16 −22.0 −18.3 −17.2 measurement method

It can be seen from Table 1 that the average power and consistency powerobtained by using SIR measurement method of the invention are all lowerthan the average power and consistency power obtained by using theconventional SIR measurement method.

FIG. 3 and FIG. 4 show diagrams of probability density and cumulativedistribution function, respectively, of transmitting power of a basestation, when making power control with the method of the invention.

Comparing the invention SIR measurement method and the conventional SIRmeasurement method, it can be seen that under the same service quality,the simulation performance of the invention power control is better thanthe simulation performance of the conventional power control. Therefore,the purpose of the invention is reached.

Above mention is only an embodiment of the invention and will not be alimit of the invention. Any equivalence change, replacement andimprovement are all included in the scope of the invention claims.

1. A signal-to-interference measurement method for a CDMA mobilecommunication system, comprising: measuring a single-path signalinterference power after single-path demodulation of a received signalin a multipath receiving device at the receiving end; equipartitioncombining a measured interference power of single-path signals to obtaintotal interference power; measuring a signal power after carrying outdiversity combination of the single-path signals; and obtaining an SIRmeasurement value by dividing the signal power by the total interferencepower.
 2. The method according to claim 1, further comprising the stepof smoothing the total interference power obtained from equipartitioncombining.
 3. The method according to claim 1, wherein the single-pathinterference power is measured in every path.
 4. The method according toclaim 1, wherein the diversity combination is a maximum ratiocombination or equivalence gain combination.
 5. An SIR measurementapparatus, comprising a RAKE combiner, a signal powermeasurement-device, interference power measurement-devices and adivider; wherein the RAKE combiner comprises multiple single-pathdemodulators and a diversity combiner, and wherein: single-path signalsoutput by the multiple single-path demodulators are all sent to thediversity combiner to carry out a multipath signal diversitycombination; a single signal, outputted from the diversity combiner, issent to the signal power measurement-device for measuring the signalpower; the interference power measurement-devices are multiple units andare all set in the RAKE combiner; a respective input of everyinterference power measurement-device is connected to a single-pathdemodulator output, and measured interference power of everyinterference power measurement-device is sent to an equipartitioncombiner for equipartition combination; and the equipartition combineroutput and output of the signal power measurement-device are sent to thedivider for division operation to obtain an SIR value.
 6. The methodaccording to claim 5, wherein the equipartition combiner is connectedwith a smoothing filter; the equipartition combiner output is sent tothe smoothing filter to carry out a smoothing operation; and, afterthat, the smoothing filter output and output of a respective said signalpower measurement-device are sent to the divider for a divisionoperation to obtain the SIR value.
 7. The method according to claim 5,wherein the multiple interference power measurement-devices and multiplesingle-path demodulators are correspondingly set one by one, arespective single-path demodulator output being connected to an input ofa respective one of the interference power measurement-devices.
 8. Themethod according to claim 5, wherein the diversity combiner is a maximumratio combiner or an equivalence gain combiner.